Question

# 1. Given that a recrystallization involving co-solvents requires that the two solvents be miscible but have...

1. Given that a recrystallization involving co-solvents requires that the two solvents be miscible but have differing polarities, which solvent pair below would be ideal for a recrystallization?

H2O and CH3OH

CH3OH and C6H14

H2O and CH3OCH3

2. The solubility of Compound A is shown below in methanol, water, ethyl acetate and toluene. Given that all of the other requirements for a recrystallization are met, which solvent would be the best for the recrystallization of 3 grams of solid A?

Water. Solubility is 8 g per 100 mL when hot and 0.2 g per 100 mL when cold

Toluene. Solubility is 2 g per 100 mL when hot and 25 g per 100 mL when cold

Ethyl acetate. Solubility is 0.2 g per 100 mL when hot and 0.1 g per 100 mL when cold

None of the solvent choices would work

Methanol. Solubility is 58 g per 100 mL when hot and 30 g per 100 mL when cold

1) Methanol is very much polar while hexane is non-polar so the two solvents are not miscible.
On the other hand the rest of the two options are miscible and polar but CH3OH has
-CH3 part which is not polar (even though the presence of -OH makes it polar) so there is
high chance of giving crystals. CH3OCH3 is polar and forms hydrogen bonding but the polarity
difference is huge
So the answer should be H2O and CH3OH

2) For toluene we can observe that solubility decreases with increase in temperature(when hot)
which reverses the reaction rate and aiding the crystallization process on a whole.
For other options the phenomena is quite opposite. So, the answer is toluene.

#### Earn Coins

Coins can be redeemed for fabulous gifts.